Photochemical stencils



United States Patent 3,383,210 PHOTOCHEMICAL STENILS Jan Pieter Poels, s Gravenwezel, Johan Lodewijk Verelst, Kontich, and Louis Maria De Haes, Edegern, Belgium, assignors to Gevaert Photo-Producten N.V., Mortsel- Antwerp, Belgium, a Belgian company No Drawing. Filed Oct. 28, 1963, Ser. No. 319,519 Claims. (CI. 96-29) This invention relates to a method of forming an improved photochemical stencil.

From the British patent specification 857,632 a method is known of forming a photochemical stencil from a stencil blank which comprises a stencil base tissue having a continuous layer of an ink impervious material comprising a proteinaceous colloid containing an agent which can re-' act with a silver halide complex to form a dispersed silver image in the colloid layer. This method comprises trans ferring a silver halide complex to the stencil blank to form imaged areas in the colloid coating thus causing a reaction to take place which releases a silver image, subsequently degrading the colloid and removing the degraded colloid in the image areas to provide stencil openings through which ink may pass.

The image-d areas in the colloid coating may be formed by the steps of exposing a silver halide coating of a negative to an original to provide a latent image of unreacted silver halide in the unexposed portions of the negative, developing the negative while in surface contact with the stencil blank with a developing solution containing a solvent for silver halide remaining in the unexposed portions of the negative to cause transfer by diffusion from the negative to the stencil coating and then separating the negative from the stencil blank.

However, according to the mentioned method of forming the imaged areas the consecutive steps are to be carried out in well determined circumstances. Moreover the obtained silver deposition in the image areas is not uniform and the silver content of the image is rather low which in its turn causes an incomplete and insufficient degradation of the colloid and removal of degraded colloid so that no high quality stencil can be obtained.

It has nOW been found that a photochemical stencil of an improved quality may be obtained by (1) image-wise exposing a silver halide material comprising in sequence a flexible base, a lightsensitive silver halide emulsion layer and a water-permeable layer, (2) pressing the said material in the presence of a developing compound, a complexing agent for silver halide, an alkali and a treating liquid against a stencil blank which contains a stencil base tissue having a continuous layer of an ink impervious material comprising a proteinaceous colloid which contains a member selected from the group consisting of development nuclei for complexed silver halide and substances capable of forming such nuclei, (3) separating the silver halide material from the stencil blank and. (4) degrading and removing the said colloid in the image areas to provide stencil openings through which ink may pass.

The process according to the present invention permits considerable variations as to the contact time between the silver halide material and the stencil blank. Moreover, by the presence of the water-permeable layer on the silver halide material a very ellicient contact is realized between the said material and the stencil blank thus causing a close and very compact silver deposition on the stencil blank which in its turn gives rise to a complete removal of colloid on those areas so that a true photochemical stencil with a high resolution is obtained.

According to the present invention it is not necessary to moisten both the image-wise exposed silver halide material and the stencil blank with treating liquid before ice pressing them against each other but it sufiices to moisten only the image-wise exposed silver halide material with said liquid and then to bring it into contact with a dry stencil blank.

The contact time between the silver halide material and the stencil blank for permitting unexposed and complexed silver halide to diffuse to the stencil blank may vary within wide limits. The best results, however, are obtained with contact times for instance comprised between 10 sec. and 10 min., preferably 2 min.

When separating the silver halide material from the stencil blank it is in many cases possible that at least a stratum of the Water-permeable layer on the silver halide material is transferred to the stencil. However, in the present process this does not give rise to complications.

The silver halide emulsion layer of the light-sensitive material for being used in a process according to this invention is preferably a hardened gelatino silver halide emulsion layer.

The water-permeable layer on the contrary is preferably a not hardened or only slightly hardened layer. Suitable binding agents for this water-permeable layer are among others one or more of the following water-permeable colloids: methyl cellulose, the sodium salt of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxyethyl starch, hydroxypropyl starch, sodium alginate, itragacanth gum, starch, poly(vinyl alcohol), poly(acrylic acid), poly(acryl amide), poly(vinyl pyrrolidone), poly(oxyethy1ene), copoly(methyl vinyl ether/maleic acid) etc. The thickness of the water-permeable layer may vary within wide limits and is dependent on the nature of the colloid used, on the occassion-al ingredients present in the said layer, on the viscosity of the colloid solution used etc. Preferably the thickness of the water-permeable layer is such that per sq. m. of light-sensitive material from 0.1 g. to 2 g. of binding agent is present. The water-permeable layer is mostly applied from an aqueous solution to which surface active compounds may have been added.

Into at least one of the constituent layers of the light sensitive material as well as into the stencil blank compounds may be incorporated influencing the formation on the stencil blank of the diffusion transfer image. Instead of being incorporated into the proteinaceous colloid of the stencil blank the development nuclei for complexed silver halide or the substances capable of forming such nuclei may also be incorporated into the treating liquid or into the water-permeable layer coated on the silver halide emulsion layer.

For more details as to the diffusion transfer image formation on the stencil blank, the degradation and removal of the colloid in the image areas to provide stencil openings, the appropriate light-sensitive material stencil blanks, treating solutions and etching solutions We refer to United Kingdom patent specification 857,632.

The following examples illustrate the present invention.

EXAMPLE 1 A light-sensitive material is prepared as follows: to a paper support of g. per sq. m. a gelatino silver chloride emulsion layer hardened in the usual way by means of formol is applied in such a way that 1.33 g. of silver chloride is present per sq. m.

Onto said light-sensitive layer a top layer is coated from the following composition:

Water ccs 1000 Hydroxyethyl starch with a substitution degree of hydroxy ethyl groups being 0.27 g 40 10% aqueous saponine ccs l0 Said layer is applied in such a way that 1 liter covers 20 sq. m.

A stencil blank is prepared by impregnating a Japanese silk paper with the following suspension:

Gelatin g 50 Water ccs 900 Colloidal silver g 0.2 Sorbitol "g Butylester of sulphonated castor oil ccs 2 aqueous formaldehyde ccs 6 The light-sensitive material is image-wise exposed to an original. Then it is passed together with the stencil blank, attached with its top margin to a supporting member of baryta-coated paper through the treating liquid of the following composition:

Water ccs 1000 Sodium sulfite (anhydrous) g 75 Sodium hydroxide g 10 Potassium bromide g 1 I-Iydroquinone g 16 1-phenyl-3-pyrazolidone g 1 Sodium thiosulphate (anhydrous) g 10 Then the stencil blank and the light-sensitive material are pressed together, kept in contact for about 2 minutes and then separated from each other. Finally the colloid in the image areas of the stencil is degraded and removed by treating the stencil with an etching solution as described in the United Kingdom patent specification 857,632.

The photochemical stencil obtained according to this process is of extremely good quality and of much better quality then a photochemical stencil obtained according to the process of the United Kingdom patent specification 857,632.

EXAMPLE 2 The process of Example 1 is repeated using, however, a light-sensitive material comprising instead of the waterpermeable layer of hydroxyethyl starch a water-permeable layer coated from the following solution:

Water ccs 1000 PAM 75 (trade name for a medium viscous poly (acryl amide) marketed by the American Cyanamide Company, New York, N.Y., U.S.A.)

g 10 10% aqeuous saponine ccs 10 This layer is applied in such a way that 1 liter covers 10 sq. m. of light-sensitive material.

The photochemical stencil obtained according to this process is also of extremely good quality.

We claim:

1. A method of forming a photochemical stencil comprising image-wise exposing a silver halide material which contains in the indicated sequence a flexible base, a lightsensitive silver halide emulsion layer and a substantially unhardened water-permeable colloid layer, pressing the said material in the presence of a developing compound, a complexing agent for silver halide, an alkali and aqueous treating liquid, against a stencil blank which contains a -stencil base tissue having a continuous layer of an inkimpervious material comprising a proteinaceous colloid which contains a member selected from the group consisting of development nuclei for complexed silver halide and substances capable of forming such nuclei, whereby the complexed silver halide diffuses from said emulsion layer through said colloid layer into contact with said stencil blank and is reduced to silver metal in the image areas of said ink impervious layer, separating the silver halide material from the stencil blank and degrading and removing the said colloid in the image areas to provide stencil openings through which ink may pass.

2. A method of forming a photochemical stencil comprising image-wise exposing a silver halide material which contains in the indicated sequence a flexible base, a hardened light-sensitive gelatino silver halide emulsion layer and a substantially unhardened water-permeable colloid layer, pressing the said material in the presence of a developing compound, a complexing agent for silver halide, an alkali and aqeuous treating liquid, against a stencil blank which contains a stencil base tissue having a continuous layer of an ink-impervious material comprising a proteinanceous colloid which contains a member selected from the group consisting of development nuclei for complexed silver halide and substances capable of forming such nuclei, whereby the complexed silver halide difluses from said emulsion layer through said colloid layer into contact with said stencil blank and is reduced to silver metal in the image areas of said ink impervious layer, separating the silver halide material from the stencil blank and degrading and removing the said colloid in the image areas to provide stencil openings through which ink may pass.

3. A method of forming a photochemical stencil com prising image-wise exposing a silver halide material which contains in the indicated sequence a flexible base, a hardened light-sensitive gelatino silver halide emulsion layer and a substantially unhardened water-permeable colloid layer containing a hydroxyalkyl starch, pressing the said material in the presence of a developing compound, a complexing agent for silver halide, an alkali and aqueous treating liquid, against a stencil blank which contains :a stencil base tissue having a continuous layer of an ink-impervious material comprising a proteinaceous colloid which contains a member selected from the group consisting of development nuclei for complexed silver halide and substances capable of forming such nuclei, whereby the complexed silver halide diffuses from said emulsion layer through said colloid layer into contact with said stencil blank and is reduced to silver metal in the image areas of said ink impervious layer, separating the silver halide material from the stencil blank and degrading and removing the said colloid in the image areas to provide stencil openings through which ink may pass.

4. A method of forming a photochemical stencil comprising image-wise exposing a silver halide material which contains in the indicated sequence a flexible base, a hardened light-sensitive gelatino silver halide emulsion layer and a substantially unhardened water-permeable colloid layer containing hydroxyethyl starch, pressing the said material in the presence of a developing compound, a complexing agent for silver halide, an alkali and aqueous treating liquid, against a stencil blank which contains a stencil base tissue having a continuous layer of an ink-impervious material comprising a proteinaceous colloid which contains a member selected from the group consisting of development nuclei for complexed silver halide and substances capable of forming such nuclei, whereby the complexed silver halide diffuses from said emulsion layer through said colloid layer into contact with said stencil blank and is reduced to silver metal in the image areas of said ink impervious layer, separating the silver halide material from the stencil blank and degrading and removing said colloid in the image areas to provide stencil openings through which ink may pass.

5. A photochemical stencil obtained according to the method of claim 2.

References Cited UNITED STATES PATENTS 2,565,376 2/1947 E. H. Land 8 2,834,676 5/1958 Stanley et al 96-29 3,067,033 12/1962 Weyde 9628 FOREIGN PATENTS 857,632 1/ 1961 Great Britain.

NORMAN G. TORCHIN, Primary Examiner.

I. TRAVIS BROWN, Examiner.

J. P. BRAMMER, Assistant Examiner. 

1. A METHOD OF FORMING A PHOTOCHEMICAL STENCIL COMPRISING IMAGE-WISE EXPOSING A SILVER HALIDE MATERIAL WHICH CONTAINS IN THE INDICATED SEQUENCE A FLEXIBLE BASE, A LIGHTSENSITIVE SILVER HALIDE EMULSION LAYER AND A SUBSTANTIALLY UNHARDENED WATER-PERMEABLE COLLOID LAYER, PRESSING THE SAID MATERIAL IN THE PRESENCE OF A DEVELOPING COMPOUND, A COMPLEXING AGENT FOR THE SILVER HALIDE, AN ALKALI AND AQUEOUS TREATING LIQUID, AGAINST A STENCIL BLANK WHICH CONTAINS A STENCIL BASE TISSUE HAVING A CONTINUOUS LAYER OF AN INKIMPREVIOUS MATERIAL COMPRISING A PROTEINACEOUS COLLOID WHICH CONTAINS A MEMBER SELECTED FROM THE GROUP CONSISTING OF DEVELOPMENT NUCLEI FOR COMPLEXED SILVER HALIDE AND SUBSTANCES CAPABLE OF FORMING SUCH NUCLEI, WHEREBY THE COMPLEXED SILVER HALIDE DIFFUSES FROM SAID EMULSION LAYER THROUGH SAID COLLOID LAYER INTO CONTACT WITH SAID STENCIL BLANK AND IS REDUCED TO SILVER METAL IN THE IMAGE AREAS OF SAID INK IMPERVIOUS LAYER, SEPARATING THE SILVER HALIDE MATERIAL FROM THE STENCIL BLANK AND DEGRADING AND REMOVING THE SAID COLLOID IN THE IMAGE AREAS TO PROVIDE STENCIL OPENINGS THROUGH WHICH INK MAY PASS. 